The invention relates to aftertreatment systems for internal combustion engine exhaust, including diesel exhaust, and more particularly to chemical species injection, and catalysis.
To address engine emission concerns, new standards continue to be proposed for substantial reduction of various emissions, including NOx and particulate emissions. Increasingly stringent standards will require installation of aftertreatment devices in engine exhaust systems. Some of the aftertreatment technologies require certain chemical species to be injected into the exhaust system. For example, HC or fuel is injected in some active lean NOx systems, and additives such as cerium and iron are injected for diesel particulate filter regeneration, and urea solution or other reductant is injected in selective catalytic reduction (SCR) systems for NOx reduction. These injected chemical species mix with exhaust gas before reaching downstream catalysts or filters.